Additive manufacturing, or three-dimensional (3D) printing, is a production technology for using an automated system to make a solid object based on a digital model. Generally, computer-aided design (CAD) modeling software is used to create the digital model of a desired solid object. Instructions for an additive manufacturing system are then created based on the digital model, for example by virtually “slicing” the digital model into cross-sections or layers. The layers can be formed or deposited in a sequential process in an additive manufacturing device to create the object.
Additive manufacturing processes offer many advantages, including potentially reducing a time period from a design phase to a prototype or commercialization phase. Design changes can be made throughout the development process based on a physical prototype rather than based on a digital model only or based on a prototype made from an expensive production tool. Generally, no specialized tooling is required because the same extrusion head in an additive manufacturing system can be used to create part composites having many different shapes, sizes and configurations. In some examples, additive manufacturing can be used to reduce a part inventory. Using additive manufacturing, some parts can be quickly made on-demand or on-site.
Various polymers can be used in additive manufacturing, including polymers having different colors, molecular weights, flame resistance characteristics, or other characteristics. Some part composites are made using a monofilament additive manufacturing technique (for example, in fused deposition modeling (FDM) or fused filament fabrication (FFF)). A monofilament can include a material strand that is about 0.1 to 3.0 mm in diameter. Some monofilament materials can bond under heat and atmospheric pressure to create a part composite that has a high degree of interaction between strand surfaces, with a small portion of voids in the bonded strands.
Various systems and methods have been proposed for regulating flow of a thermoplastic material in an additive manufacturing system. Batchelder et al., in U.S. Pat. No. 6,578,596, titled “Apparatus and Method for Thermoplastic extrusion”, refers to a thermoplastic flow channel, in an extrusion head, that extends from a thermoplastic supply manifold to a discharge orifice. Batchelder et al. further refers to using a coolant at an intermediate location between the supply manifold and the discharge orifice to open or close the flow channel. Labossiere et al., in U.S. Pat. No. 7,604,470, titled “Single-motor Extrusion Head Having Multiple Extrusion Lines”, refers to supplying cooling air from an airflow manifold to cool an extruded flow of material to improve fusion with previously-deposited material.